WASHINGTON (AP) — The Obama administration appeared to be in the dark Thursday about a hostage situation at a natural gas plant in Algeria, where Algerian forces launched a military assault to free dozens of foreign hostages, including an unknown number of Americans, held by Islamist militants.

An administration official said the U.S. was not aware of the raid to free the hostages in advance. The U.S. was offering no details about how many American hostages had been taken and whether they were still in captivity or even alive.

The U.S. condemned the militants for seizing the isolated plant 800 miles south of the capital, Algiers, in the Sahara Desert.

Militants with the Masked Brigade, a Mali-based al-Qaida offshoot that has been speaking through a Mauritanian news outlet, said the Algerians opened fire Thursday as the militants tried to leave the vast Ain Amenas energy complex with their hostages. They claimed that 35 hostages and 15 militants died but seven hostages survived when Algerian helicopters strafed their convoy.

Secretary of State Hillary Rodham Clinton said U.S. counterterrorism officials were in touch with their Algerian counterparts and that she planned to speak Thursday with Algerian Prime Minister Abdelmalek Sellal for the second time in as many days. She made a vague reference to ongoing U.S. “planning,” without elaborating.

“The security of our Americans who are held hostage is our highest priority,” Clinton told reporters. “Because of the fluidity and the fact that there is a lot of planning going on, I cannot give you any further details.”

“This is a serious and sensitive situation,” Pentagon spokesman George Little told reporters traveling with Defense Secretary Leon Panetta in England. Little said military officials were actively seeking information, and that Panetta had been briefed by senior military officials.

Ahead of the raid, U.S. officials had been urging the Algerians to be cautious in their actions, but did not know a rescue mission was planned, said the administration official, who spoke on the condition of anonymity because they were not authorized to speak publicly.

Militants earlier said they were holding seven Americans, but the administration confirmed only that Americans were among those taken.

“We are deeply concerned about any loss of innocent life and are seeking clarity from the government of Algeria,” White House press secretary Jay Carney told reporters.

During her conversation with Algeria’s prime minister Wednesday, Clinton expressed Washington’s “willingness to be helpful,” State Department spokeswoman Victoria Nuland said. They also discussed what type of assistance might be needed, Nuland added, but declined to provide details.

A senior U.S. military official said the military offered Algeria hostage-rescue teams on Wednesdays, but the offer was refused. The official spoke on condition of anonymity because he wasn’t authorized to discuss the offer publicly.

Nuland said the United States also was in contact with American businesses across North Africa and the Middle East to help them guard against the possibility of copycat attacks.